* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: "微软雅黑 Light" ,sans-serif;
}

html,
body {
    display: grid;
    height: 100vh;
    width: 100%;
    place-items: center;
    background: linear-gradient(
            to right top,
            #59a59d,
            #448a86,
            #316f6e,
            #1e5658,
            #0b3e41
    );
}

::selection {
    background: #ff80bf;
}

.container {
    background: #fff;
    max-width: 350px;
    width: 100%;
    padding: 25px 30px;
    border-radius: 5px;
    box-shadow: 0 10px 10px rgba(0, 0, 0, 0.15);
}
.container form .title {
    font-size: 30px;
    font-weight: 600;
    margin: 20px 0 10px 0;
    position: relative;
}
.container form .title:before {
    content: "";
    position: absolute;
    height: 4px;
    width: 33px;
    left: 0px;
    bottom: 3px;
    border-radius: 5px;
    background: linear-gradient(
            to right top,
            #59a59d,
            #448a86,
            #316f6e,
            #1e5658,
            #0b3e41
    );
}
.container form .input-box {
    width: 100%;
    height: 45px;
    margin-top: 25px;
    position: relative;
}
.container form .input-box input {
    width: 100%;
    height: 100%;
    outline: none;
    font-size: 16px;
    border: none;
}
.container form .underline::before {
    content: "";
    position: absolute;
    height: 2px;
    width: 100%;
    background: #ccc;
    left: 0;
    bottom: 0;
}
.container form .underline::after {
    content: "";
    position: absolute;
    height: 2px;
    width: 100%;
    background: linear-gradient(
            to right top,
            #59a59d,
            #448a86,
            #316f6e,
            #1e5658,
            #0b3e41
    );
    left: 0;
    bottom: 0;
    transform: scaleX(0);
    transform-origin: left;
    transition: all 0.3s ease;
}
.container form .input-box input:focus ~ .underline::after,
.container form .input-box input:valid ~ .underline::after {
    transform: scaleX(1);
    transform-origin: left;
}
.container form .button {
    margin: 40px 0 20px 0;
}

.container .input-box input[type="submit"] {
    background: linear-gradient(
            to right top,
            #59a59d,
            #448a86,
            #316f6e,
            #1e5658,
            #0b3e41
    );
    font-size: 17px;
    color: #fff;
    border-radius: 5px;
    cursor: pointer;
    transition: all 0.3s ease;
}
.container .input-box input[type="submit"]:hover {
    letter-spacing: 1px;
    background: linear-gradient(
            to right top,
            #59a59d,
            #448a86,
            #316f6e,
            #1e5658,
            #0b3e41
    );
}